arXiv subjects

François Richard

Publications and source records attributed to François Richard.

17 recordsLinked to original sources

arXiv2026

A strategy for a Kaluza-Klein graviton discovery at LHC

Evidence for excesses observed at LHC tend to cluster mostly around 95 GeV and 650 GeV. We claim that a consequent interpretation of the 650 GeV and some additional indications calls for a Randall Sundrum sequence of Kaluza Klein graviton resonances. A common prejudice claims that such resonances should be very heavy, out of reach for LHC. We argue that this is no so. Although present LHC searches seem to exclude these particles below 2 TeV, we explain why this 650 GeV resonance could be one of them. We also explain why ongoing analyses ignore this scenario and apply selections which are only valid for scalar resonances. This could also apply to ongoing searches for Higgs pairs where the search for resonances decaying into SM Higgs pairs ignores the KK graviton scenario. We expect that with a correct treatment, one could very significantly increase the detection efficiency for ZZ and hh channels and achieve, with present data, a convincing proof of our expectations. Channels like h(95)h(125) and h(95)h(95) should be added to present selections. Such improvements should allow to reach a discovery. For the ZZ and WW channels, one can use semi-leptonic and purely hadronic final states, to confirm the tower of KK resonances indicated up to 3 TeV.

hep-ph↗

arXiv2026

Influence of the KK graviton decay into hh on the triple Higgs measurement at LHC

Evidence for two KK graviton candidates has been previously reported at 380 GeV and 700 GeV. They would provide graviton factories in an e+e- collider. Following a Randall Sundrum interpretation, two extra resonances should appear at 1000 GeV and 1322 GeV. Recently ATLAS, in its search for triple Higgs coupling, has reported an excess in that mass region which comforts this prediction. Local cross sections are therefore clearly in excess of the standard predictions which implies muHH>1. While still marginally significant, this effect appears in a mass region with low background which allows to expect good prospects of discovery with RUN3 data. Such a result could therefore allow to confirm the existence of a series of KK graviton resonances observable at LHC. An optimised strategy, which includes H(95) is proposed to do so. Other opportunities appear in searches for heavier KK graviton recurrences decaying into ZZ/WW in semi-leptonic and fully hadronic modes. Prospects for measuring heavy KK graviton decays GKKi->G380G380 at HL-LHC are discussed. Indirect evidences for the RS model coming from precision measurements are also presented. KK lower mass limits for other KK particles are deduced from precision measurements at LEP/SLC and LHC.

hep-ex↗

arXiv2026

A DM candidate indicated at Fermi-LAT and LZ ? Connection with LHC and LC prospects

Recently an analysis of Fermi-LAT data has claimed a significant excess of energetic photons centred around 20 GeV, in the halo of our galaxy but absent in dwarf galaxies. This excess can be interpreted as coming from dark mater (DM) objects with a mass of few 100 GeV which annihilate into hadronic jets containing photons mainly from neutral pions. This observation is independently backed up by a completely independent observation of the LUX-ZEPLIN (LZ) detector of a DM candidate in the same region of mass. To avoid contradiction with upper limits coming from dwarf galaxies, one is led to assume the presence of a spin 2 resonance coupled to these objects, which explains this difference as due to different speed distributions in the two regions. This work recalls that LHC data indicate a tower of Kaluza Klein graviton resonances. This solution is at variance with a SUSY interpretation of DM and therefore does not necessary call for a 1.1 TeV Higgsino, as often proposed. If these KK resonances are coupled to e+e-, as indicated by LHC data, an e+e- collider could observe these DM objects. LHC could confirm our KK graviton interpretation and, eventually, detect the DM particles. This would allow to define de energy needed at a future e+e- collider.

hep-ph↗

arXiv2026

Evidence for BSM spin 0 and spin 2 resonances at LHC Possible Interpretations

Nine statistically significant decay channels are observed in LHC data around a mass of 650 GeV. We interpret three of them as coming from a 20 GeV wide resonance observed in e+e-, 2 photons and ZZ into four leptons which could be a J=2 Kaluza Klein graviton resonance called T700 (T for tensor with J=2). This hypothesis is reinforced by noting that this signal is produced by VBF and not by ggF since it disappears in ZZ when treated as a scalar. Given that the six other excesses have poor mass resolution, one cannot exclude the presence of an additional wide scalar resonance called H650. Assuming a Randall Sundrum RS model, we conclude that LHC observes the predicted sequence T380, T700 and T1000, with prospects to discover heavier states by reconstructing hadronic states. At variance with the RS model, T700 decouples from gluon and photon pairs, suggesting a composite model interpretation in which preons are charge neutral and colourless. T700 does significantly couple to $e^+e^-$ which has implications for future $e^+e^-$ colliders. Perturbative unitarity requirements predict $T^{++} \to W^+W^+$ and $T^+ \to ZW$ resonances, again indicated by LHC data. With BR($e^+e^-$)~0.25%, measured by ATLAS and CMS, this scenario offers excellent prospects for abundantly (Gigafactory) producing a sequence of narrow resonances at future $e^+e^-$ colliders. For heavy scalars, the situation is less clear. Following ATLAS and CMS, we expect that the top loop contribution to the gluon-gluon fusion mechanism $ggF$ could produce a deficit rather than an excess in the mass distribution of top pairs, which prevents a standard estimate of the statistical significance for heavy resonances. It seems that the pseudo-scalar and scalar resonances A490 and H650, indicated by other channels, create observable deviations in the $t \bar t$ analyses presented by ATLAS and CMS.

hep-ph↗

arXiv2025

X650 $\to$ ZZ/WW/H125H95/A450Z/$γγ$ -- $J=1$, $J=2$, narrow or wide resonance?

At ICHEP 2024 CMS has published RUN2 results for ZZ->4 leptons and reached the conclusion that there is no evidence for a scalar resonance H650 decaying into ZZ, as was also concluded by ATLAS using an MVA analysis optimised for a scalar particle. Since this resonance is indicated into ZZ by ATLAS in a Cut Based Analysis and into three other modes: WW and h95h125 by CMS, ttZ by ATLAS , the present paper is an attempt to understand these apparent contradictions. Our conclusion is that strict selections for the reaction H650->ZZ cut as much into the signal than into the background, therefore reducing its statistical significance. A plausible interpretation of this behaviour is that these selections are inadequate for a spin 2 particle produced by the VBF process and decaying into ZZ with an angular distribution similar to the Drell Yan background. If true, our description of the various findings in term of the Georgi Machacek model needs to be deeply revised, which is attempted in the present note. A scenario with T690 as a spin 2 narrow resonance is presented which naturally accommodates WW/ZZ and h95h125 decays, while we suggest that A450Z could come from a H650 nearby resonance. We propose a scheme in which scalar resonances are accommodated in three scalar isodoublets, while T690, T450++, T375+ and T350 belong to two tensor isoquintuplets. In this scenario, T690 could be a narrow resonance which interferes with the SM background, as confirmed by its observation in the two photon mode, reinforcing a Kaluza Klein graviton interpretation. If, as indicated by ATLAS and CMS, T690 couples to e+e-, this scenario leads to a dramatic prediction for future $e^+e^-$ colliders.

hep-ph↗

arXiv2024

Triple Higgs couplings at LHC

A global interpretation of several significant indications of scalar resonances observed at LHC is achieved using the Georgi Machacek model. Among many other consequences, one predicts large cross sections for the processes ggFH(320)->h(125)h(125) and A(151)A(151) and ggF->A(420)->H(320)Z, where H(320) has been observed in A(420)->H(320)Z->bbbbl+l- and where A(151) is observed into two photons accompanied by a b jet, a lepton or missing transverse energy. We predict that ggF->H(320) has a cross section of about 2000 fb with a BR into h(125)(125) of 17% and into A(151)A(151) of 45%. Henceforth we predict that ggF->H(320)->hh will dominate over the SM process h*->hh, where h is the SM h(125) scalar. One expects that H(320)->A(151)A(151) can be observed into bbbb, becoming one of the most significant BSM phenomena identified so far. Arguments in favor of a SUSY version of GM are also provided.

hep-ph↗

arXiv2024

H(650) -> W+W-/ZZ predicts H++ -> W+W+ and H+ -> ZW+, as indicated by LHC data

Several indications for neutral scalars are observed at the LHC. One of them, a broad resonance peaked at about 650 GeV which we call H(650), was first observed by an outsider combining published histograms from ATLAS and CMS on ZZ -> 4 leptons searches, and this combination shows a local significance close to 4 s.d. Since then, CMS has reported two other indications at the same mass, with similar local significances: H->WW->2leptons+neutrinos and H(650)->bbh(125) where mbb~90 GeV and h(125)->gam gam. ATLAS has completed its analysis of ZZ->4 leptons from which we infer an indication for H(650) with 3.5 s.d. significance. Combining these three results, one gets a global statistical significance above 6 s.d. H(650) has a coupling to WW similar to h(125) and therefore we argue that a sum rule (SR) required by unitarity for W+W- scattering implies that there should be a compensating effect from a doubly charged scalar H++, with a large coupling to W+W+. We therefore predict that this mode should become visible through the vector boson fusion process W+W+->H++, naturally provided by LHC. A recent indication for H++(450)->W+W+ from ATLAS allows a model independent interpretation of this result through the SR constraint which gives BR(H++->W+W+)~10%, implying the occurrence of additional decay modes H+W+ and H+H+ from one or several light H+ with masses below mH++ - mW or MH++/2, that is mH+ < 370 GeV or 225 GeV. A similar analysis is performed for H+(375)->ZW, indicated by ATLAS and CMS. Both channels suggest a scalar field content similar to the Georgi Machacek model with triplets, at variance with the models usually considered. Implications on precision measurements are presented followed by a complete extraction of the GM parameters. An alternate interpretation of the 650 GeV resonance as a tensor is also briefly discussed. Implications for precision measurements are presented.

hep-ph↗

arXiv2022

Searches for scalars at LHC and interpretation of the findings

In view of the future Higgs factories, this work presents the status of scalar searches at the LHC with an emphasis on the H(650) resonance which has been observed in WW, ZZ and h(95)h(125) channels, with a cumulative evidence of about 7 s.d. global significance. Its interpretation in models, restricted to extension of the scalar sector by SU(2) singlets and doublets, is clearly excluded, while its interpretation in models with additional triplets requires an extension with respect to the conventional Georgi-Machacek model. A general picture of these searches is updated, showing that h(95) is also reaching a similar level of evidence while two other candidates, A(400) and h(151), although less prominent, are above the 4 s.d. global evidence.

hep-ph↗

arXiv2022

A Georgi-Machacek Interpretation of the Associate Production of a Neutral Scalar with Mass around 151 GeV

Following an investigation of several indications for new physics from LHC data, a detailed exploration of the Georgi-Machacek (GM) model was elaborated in a previous publication. This framework is used here to interpret the findings of Crivellin et al., which were obtained by combining the 2 photon mass spectrum from ATLAS and CMS, adding extra conditions, the most efficient one being the presence of >90 GeV missing transverse energy. The claim is a ~5 s.d. excess at 151 GeV. The GM model naturally explains this as coming from the cascade A(400)->H(151)Z, where H(151) is an isosinglet predicted by GM and where the accompanying signal comes from the decay of a Z boson into neutrino pairs. Satisfying the constraints from LHC measurements of the ZWW channel, which can receive a large contribution from this cascade, suggests that H(151) could dominantly decay into two light CP-odd scalars, following an ATLAS indication for h(125) decaying into bbmumu. A spectacular occurrence of signals is predicted at an $e^+e^-$ collider operating up to 1 TeV, an energy sufficient to cover the whole scenario.

hep-ph↗

arXiv2021

Global interpretation of LHC indications within the Georgi-Machacek Higgs model

Following various LHC indications for new scalars, an interpretation of these is given in terms of the Georgi-Machacek (GM) model. On top of the confirmed SM Higgs boson, there are indications for a light Higgs at 96 GeV, for a CP-odd boson at 400 GeV, A(400), and for a heavy Higgs boson at 660 GeV. An extension of the GM is needed to interpret the fermion couplings of A(400). Potentially interesting deviations are also observed in the ttW cross-section measurement, which naturally fit into this picture. None of them crosses the fatidic five s.d. evidence but the addition of these effects, consistent with GM, suggest that there are good hopes for solid discoveries at HL-LHC, which should boost the motivation for future machines. The GM model also provides a useful framework to estimate the rates expected for various channels at an $e^+e^-$ collider, together with the range of energies needed. ILC performances are used for a quantitative estimate of these rates for the prominent channels.

hep-ph↗

arXiv2020

Indications for extra scalars at LHC? -- BSM physics at future $e^+e^-$ colliders

This paper intends to collect available data on searches for scalar resonances at LHC. It is suggested that, in the absence of SUSY, the most compelling picture is the composite framework, with the idea that the lightest particles are composite scalars of the pseudo-Nambu-Goldstone type, emerging from a broken symmetry at a higher scale, the h(125) boson being one of them. Searches in two-photons, Z-photon, ZZ into 4 leptons, top, h and W pairs are reviewed. A recent search based on lepton tagging from a spectator W/Z is also discussed. Aside from the already well-known scalar observed by CMS and LEP2 at 96 GeV, I discuss the evidence and the interpretation for a possible resonance observed in ZZ around 700 GeV by CMS and ATLAS and some evidence for a CP-odd scalar at ~400 GeV. Future searches at HL-LHC and at $e^+e^-$ colliders are briefly sketched.

hep-ex↗

arXiv2017

Scalar Production in Association with a Z Boson at LHC and ILC: the Mixed Higgs-Radion Case of Warped Models

The radion scalar field might be the lightest new particle predicted by extra-dimensional extensions of the Standard Model. It could thus lead to the first signatures of new physics at the LHC collider. We perform a complete study of the radion production in association with the Z gauge boson in the custodially protected warped model with a brane-localised Higgs boson addressing the gauge hierarchy problem. Radion-Higgs mixing effects are present. Such a radion production receives possibly resonant contributions from the Kaluza-Klein excitations of the Z boson as well as the extra neutral gauge boson (Z'). All the exchange and mixing effects induced by those heavy bosons are taken into account in the radion coupling and rate calculations. The investigation of the considered radion production at LHC allows to be sensitive to some parts of the parameter space but only the ILC program at high luminosity would cover most of the theoretically allowed parameter space via the studied reaction. Complementary tests of the same theoretical parameters can be realised through the high accuracy measurements of the Higgs couplings at ILC. The generic sensitivity limits on the rates discussed for the LHC and ILC potential reach can be applied to the searches for other (light) exotic scalar bosons.

hep-ph↗

arXiv2015

Diboson resonances within a custodially protected warped extra-dimensional scenario

We propose an interpretation of the diboson excess recently observed by the ATLAS and CMS collaborations in terms of Kaluza-Klein excitations of electroweak gauge bosons stemming from a realization of a warped extra-dimensional model that is protected by a custodial symmetry. Besides accounting for the LHC diboson data, this scenario also leads to an explanation of the anomalies that have been observed in the measurements of the forward-backward asymmetries for bottom quarks at LEP and top quarks at the Tevatron.

hep-ph↗

arXiv2013

A Z-prime interpretation of Bd->K*mu+mu- data and consequences for high energy colliders

In this note, I examine the possible consequences for high energy colliders of a Z-prime interpretation of the LHCb anomaly observed in the K*mu+mu- final state. Two examples are elaborated in the framework of the so-called 331 model. In the first one it is shown that LEP2 provides the tightest lower mass limit for the Z-prime boson, above 8 TeV, while in the second one the lower mass limit is set by ATLAS/CMS to about 3 TeV. It is then shown that precision measurements at ILC 500 GeV can fully explore the underlying structure of the model by measuring the fermion final states separately: leptons, charm, beauty and top final states. Z-prime-Z mixing can also be substantial, thus leading to possible effects almost observable at LEP1 and which can be precisely measured at GigaZ. Discovery prospects for heavy bosons and heavy fermions at LHC are also discussed .

hep-ph↗

arXiv2013

Can LHC observe an anomaly in ttZ production?

The cross section for production at the 7 TeV LHC has been measured. For the first time it therefore becomes possible to measure Z couplings to top quarks. Interpreting the notorious LEP1 anomaly on Z couplings to b quarks in terms of an extra-dimension model, one expects an excess, as large as a factor 2, on the rate which may already become significant with the LHC at 8 TeV data. Other schemes are reviewed which also predict deviations of couplings. The size of the effect and a dramatic increase of the top quarks with the right chirality should confirm our interpretation of the underlying mechanism. Complementary signals observable at LHC are also briefly reviewed.

hep-ph↗

arXiv2012

Determination of Top-quark Asymmetries at the ILC

A study of top quark production at the future International Linear Collider, ILC, with a centre-of-mass energy of 500 GeV is presented. The emphasis is put on determining the sensitivity to physics beyond the Standard Model. The analysis has been carried out with a full simulation of the ILD detector. Both, the forward-backward asymmetry and the left-right asymmetry can be determined to a precision of about 1% to 1.5%. The analysis points out an ambiguity which arises in case of the production of top-quarks with left-handed helicity.

hep-ex↗

arXiv2007

Aid to Percutaneous Renal Access by Virtual Projection of the Ultrasound Puncture Tract onto Fluoroscopic Images

Background and Purpose: Percutaneous renal access in the context of percutaneous nephrolithotomy (PCNL) is a difficult technique, requiring rapid and precise access to a particular calix. We present a computerized system designed to improve percutaneous renal access by projecting the ultrasound puncture tract onto fluoroscopic images. Materials and Methods: The system consists of a computer and a localizer allowing spatial localization of the position of the various instruments. Without any human intervention, the ultrasound nephrostomy tract is superimposed in real time onto fluoroscopic images acquired in various views. Results: We tested our approach by laboratory experiments on a phantom. Also, after approval by our institution's Ethics Committee, we validated this technique in the operating room during PCNL in one patient. Conclusion: Our system is reliable, and the absence of image-processing procedures makes it robust. We have initiated a prospective study to validate this technique both for PCNL specialists and as a learning tool.

physics.med-ph↗